Thin film magnetic element

ABSTRACT

A thin-film magnetic element is formed of a substrate, a first thin film coil made of a conductive material and formed in a spiral shape on the surface of the substrate parallel thereto, and a second thin-film coil made of a conductive material and formed in a spiral shape on the first thin-film coil parallel to the substrate. The first thin-film coil and the second thin-film coil occupy nearly the same position relative to the substrate surface. Each of the first and second thin film coils changes a line width from an inner circumference to an outer circumference, and a changing ratio of the line width at the first thin film coil is different from that at the second thin film coil. The spiral shapes of the first and second thin-film coils are shifted slightly away from each other in a direction parallel to the substrate surface.

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional application of patent application Ser. No.08/025,422 filed on Mar. 1, 1993, now U.S. Pat. No. 5,355,301.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to an extremely small one-chip switchingpower supply device formed of magnetic inductive elements, such as atransformer with a thin-film laminated construction and a reactormounted on a semiconductor chip.

Switching power supply devices used widely as DC constant voltage powersupply or stabilized power supply devices for electronic devices includea variety of circuitries, such as so-called forward-type, flyback-typeand chopper-type devices. In the above systems, the input side and theoutput side are linked via magnetic inductive elements and devices, suchas a transformer and an inductor, and a direct voltage on the outputside is maintained constant at all times while turning on and off theinput side current in the magnetic induction elements by switchingelements such as transistors and controlling the duty ratio.

Since these switching power supply devices require rectification diodes,smoothing capacitors and controlling integrated circuit devices inaddition to such magnetic induction elements and switching elements asdescribed above, these circuit parts have all been mounted normally on aprinted wiring substrate. However, as electronic devices continue toenlarge in scale and become more complex, wherein switching power supplydevices with small capacities from several watts to ten watts areincorporated in electronic circuits for constituting such devices,switching power supplies that are as small and as inexpensive aspossible have been in demand.

To meet such a demand, recent advanced high integration techniques canbe utilized to incorporate all the semiconductor elements required inthe switching power supply devices including switching elements andrectification diodes, in addition to the conventional control circuitsinto one single chip as small as 10 mm square or less in an integratedcircuit device. In addition, the size of the magnetic induction elementsand the smoothing capacitors can be decreased to nearly half of that inthe conventional products by raising the switching frequencies for thecircuit operation to several hundred kHz or higher, while elevatingtheir effective reactance value.

Rationalization of the switching power supply devices has beenpreviously advanced by integrating semiconductor elements and activeelements on a single chip, and reducing the sizes of the transformersand smoothing capacitors by raising the switching frequencies asdescribed above. However, these methods of solving the existing problemsare approaching to their limit in terms of performance and reliabilityas explained below.

That is, even if the constituent parts are reduced in size and thenumber of parts is reduced, the way they are mounted on a printed wiringsubstrate is still the same. The mounting process is not eliminated evenif the number of parts is reduced. Rather, the mounting work becomesmore difficult as the parts become smaller, and hence the amount oflabor actually required does not change much. In addition, since theactive elements are connected to the passive elements via the wiring onthe printed substrate, if the switching frequency exceeds 1 MHz, thedevice performance tends to vary because the circuit operation isaffected by the wiring inductance, and the device tends to malfunctionmore easily because of incoming noise picked up by the wiring. Hence,the device reliability decreases. As a result, it is difficult to raisethe switching frequency to about 1 MHz.

Another problem is that, when the switching frequency exceeds 1 MHz, thefrequency characteristics of the magnetic inductive elements deteriorateto cause a saturation of the inductance value. That is, while it ispossible to draw out an output in proportion to the square root of thefrequency from the magnetic inductive elements with a certain size in afrequency region near 100 k Hz, and to obtain a reactance valueproportional to the frequency, high-frequency loss increases in themagnetic circuits of the magnetic inductive elements in a high frequencyregion greater than 1 MHz, and the electrostatic capacity distributedinternally increases. Therefore, since the frequency characteristic inthe inductance value gradually deteriorates, and the reactance valuewhich is a multiplicity of the inductance value and the angularfrequency is saturated in a high frequency region greater than 10 MHzand increases very little, it becomes impossible to reduce the size ofthe magnetic inductive elements beyond a certain limit.

Still another problem is that, as the switching frequency increases, thehigh frequency loss in the switching element also increases. Forexample, the analysis results of losses in a switching power supplydevice of a flyback type operated at a switching frequency of 1 MHzindicate that the loss in the switching element accounted for 35% of thetotal loss, while the magnetic inductive element accounted for 20%, andother parts accounted for the remaining 45%. Meanwhile, the loss in theswitching element is the largest, and this tends to form a bottleneck asthe frequency is raised.

The present invention is intended to overcome such limits or theformation of the bottleneck, while providing a switching power supplydevice that is capable of further reducing the size and ensuring a highconversion efficiency.

SUMMARY OF THE INVENTION

The above objects can be achieved according to the present invention bya one-chip switching power supply device that has a voltage-convertingsection formed of a magnetic inductive element with a thin-filmstructure, a switching element to turn the input current of thevoltage-converting section on and off, and a voltage-controlling sectionto control the switching element so that the output side voltage in thevoltage-converting section is kept constant at the desired value,wherein an active element containing the switching element and thecircuit elements in the voltage-controlling section is incorporated in asingle semiconductor chip, and a wiring layer connecting the activeelements on the semiconductor chip and the voltage-converting sectionconnected thereto is laminated sequentially via insulation films.

While the circuitry of the switching power supply device with the aboveconstruction may be used either for forward-type, flyback-type orchopper-type systems, it is especially advantageous to use flybacktransformers in the magnetic inductive elements of the voltageconverting section to keep the constant voltage performance of theoutput side voltage high, and to simplify the entire construction. It isalso advantageous to use insulated gate-controlling elements, such asfield-effect transistors and insulated-gate bipolar transistors toprovide insulation across the input and the output. It is especiallyadvantageous to use a frequency of 1 MHz or higher, more preferably 10MHz or higher, as a switching frequency to turn the input side currentin the voltage-converting section on and off when reducing the size ofthe device. It is also recommended that, when incorporating capacitorsin the device to smooth the output voltage, the capacitors are builtinto a wiring layer by utilizing a wiring aluminum film or an insulationfilm.

Furthermore, in order to reduce the high frequency loss in the switchingelement and raise the conversion efficiency of the device, it isadvantageous to split at least the input side of the voltage-convertingsection into two or more sections to independently turn the input sidecurrent flowing through each split input section on and off using theswitching elements commonly controlled by the voltage controllingsection. In this case, it is possible to split only the input side intotwo or more sections while the magnetic inductive elements in thevoltage-controlling section can remain as a single part. However, it ismore advantageous to dispose various magnetic inductive elements so thatthe switching element will turn its input side current on and offindependently, and moreover, connect the various magnetic inductiveelements in series at their output side to draw out the output sidevoltage, thereby strengthening the magnetic bond between the input sideand the output side.

When various magnetic inductive elements are to be arranged, it isnecessary to make each element as small as possible. To achieve thisobjective, it is advantageous to split the thin-film conductors on theinput side and the output side into two or more layers (usually two) inthe vertical direction, when reducing the area of each magneticinductive element, reducing the crossing points between the thin-filmconductors, and raising the magnetic bond coefficient between the inputside and the output side when connecting in series the output sides ofthe various magnetic inductive elements in which the amount of windingon each magnetic inductive element varies considerably.

The thin-film conductors used as the magnetic inductive elements in thecoils of transformers and reactors should be set in a spiral or zigzagform to raise the area efficiency. In particular, the latter pattern hasan advantage in that it reduces the high frequency loss in a magneticcircuit, while because it is constructed simply, the former isespecially advantageous for strengthening the magnetic bond between theinput side coil and the output side coil in a transformer to raise theoutput that can be drawn out from a transformer of a certain size.

Using magnetic thin films made of ferromagnetic metals with softmagnetism is advisable for iron cores in the magnetic inductive element,and making the magnetic inductive element to have a shell-typeconstruction using the thin magnetic films for sandwiching the thin filmconductor for the coil can advantageously reduce the magnetism leakageproblem. In

In addition, it is especially advantageous to use amorphous magneticmetals for the thin magnetic films and to cut a large number of narrowslits on the film in a direction perpendicular to the thin filmconductor for the coil to reduce the high frequency loss in the magneticcircuit and to raise the high frequency characteristics of theinductance values of the magnetic inductive element.

The present invention makes it possible to reduce the size of theswitching element mounted on a semiconductor chip of an integratedcircuit because all the active elements including the switching elementare integrated in a single semiconductor chip. Moreover, the switchingfrequencies can be raised beyond the conventional limit by employing athin-film laminated structure in a magnetic inductive element in thevoltage-converting section, which is indispensable for a switching powersupply device, and reducing the size of the switching power supplydevice while solving the problems centering around the printed wiringsubstrates by mounting the thin voltage-converting section on thesemiconductor chip of an integrated circuit via a wiring layer toarrange the section in a one-chip construction. Furthermore, themanufacture of the device can be rationalized by eliminating the partsto be mounted and device assembly.

Further, it is necessary, in addition to size reduction, to raise theconversion efficiency in a switching power supply device by suppressinghigh frequency losses. Since the loss in a switching element is largestamong the losses in the components of the device, it is especiallyadvantageous to split the input side of the voltage-converting sectioninto two or more sections so that the switching element turns the inputside current flowing in the split input sections on and offindependently, thereby reducing the current rating for the switchingelement. In addition, this would raise the operating speed, so that theswitching loss would be reduced.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1(a) shows a circuitry of a flyback-type power supply device of theinvention;

FIG. 1(b) shows a circuitry of a forward-type power supply device of theinvention;

FIG. 1(c) shows a circuitry of a chopper-type power supply device of theinvention;

FIG. 2 shows a sectional perspective view of a part of the one-chipconstruction of a flyback-type switching power supply device accordingto the present invention;

FIG. 3(a) is a partly cut top view of a thin-film laminated constructionof magnetic inductive elements in a voltage-converting section referringto a flyback-type transformer;

FIG. 3(b) is a section view taken along line 3(b)-3(b) of FIG. 3(a);

FIG. 4 is a circuit diagram for a different embodiment of the presentinvention, in which various switching elements and magnetic inductiveelements in the voltage-converting section are disposed;

FIG. 5 is a top view of a chip showing an arrangement of variousmagnetic inductive elements and their related parts corresponding to theembodiment in FIG. 4;

FIG. 6(a) is a top view of a lower layer of a thin-film conductor incase coils of the magnetic inductive elements in the embodiment in FIG.4 is split into upper and lower layers;

FIG. 6(b) is a top view of an upper layer of a thin-film conductor incase coils of the magnetic inductive elements in the embodiment in FIG.4 are split into upper and lower layers;

FIG. 7 is a section view for showing critical parts of a thin-filmtransformer according to the present invention;

FIG. 8(a) is a section view for showing critical parts of the thin-filmtransformer of FIG. 7;

FIG. 8(b) is a section view for showing critical parts of the thin-filmtransformer according to another version of FIG. 7;

FIG. 9 is a section view for showing critical parts of the thin-filmtransformer according to a different embodiment of FIG. 7;

FIG. 10 is a graph showing a relationship between a parameter "k"defining a spiral shape of a thin-film coil in the thin-film transformershown in FIG. 9 and a self-inductance L;

FIG. 11 is a graph showing a relationship between a parameter "k"defining a spiral shape of a thin-film coil in the thin-film transformershown in FIG. 9 and a resistance R;

FIG. 12 is a graph showing a relationship between a parameter "k"defining a spiral shape of a thin-film coil in the thin-film transformershown in FIG. 9 and a value Q; and

FIG. 13 is a plan view showing critical parts of a thin-film inductoraccording to a different embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Explanation will be made for the embodiments of the present inventionwith reference to the drawings. FIG. 1 illustrates the circuitries ofthe major circuit systems of the switching power supply devicesaccording to the present invention, wherein FIG. 1(a) shows a flybacktype, FIG. 1(b) shows a forward type, and FIG. 1(c) shows a choppertype. Although the circuitries have been well known in the art, thebrief explanation is made below.

In the circuitry as shown in FIG. 1(a), a magnetic inductive element ina voltage-converting section (30) shown in the upper part of the figureis for the flyback transformer (31), wherein the present invention usesa thin magnetic film in an iron core or a magnetic circuit (32), andthin conductive films in a primary coil (34) and a secondary coil (35),respectively. In the example shown in the figure, an alternating voltageis received by the input terminal (Ti), rectified by a rectificationcircuit (41) and smoothed by the capacitor (42) to become a directvoltage which is then supplied to the primary coil (34) in thetransformer (31). An alternating voltage generated by the secondary coil(35) in the transformer (31) is rectified by the rectification diode(44), while the current flowing through the transformer is controlledinterruptively by the switching element (43) as usual. The voltage issmoothed into a stabilized direct voltage by the capacitor (46) and isthen outputted from the output terminal (To) to the load.

In the present invention, insulation gate controlled semiconductors,such as field-effect transistors and insulated gate bipolar transistors,are used for the switching element (43) as shown in the figure, in whichthe gates are controlled by the voltage-controlling section (47) toperform switching operations. The voltage-controlling section (47)includes an oscillation circuit to determine the switching frequenciesas usual, wherein frequency is 1 MHz or higher or more preferably 10 MHzor higher in the present invention. The voltage-controlling section (47)receives the actual values of the output voltage detected by thevoltage-detecting circuit (48), which is formed of a pair of resistorsas shown in the figure, and which plays a role in controlling theswitching element (43) so that the voltage value remains at the desiredvalue as usual, the circuit being a CMOS-type integrated circuit, forexample.

The forward-type switching power circuit in FIG. 1(b) uses an ordinarytransformer (31), its secondary alternating voltage being changed by adiode (44) into a direct voltage which is smoothed by a reactor (37) anda capacitor (46) before it is outputted from an output terminals (To).In this case, the diode (45) is connected to permit free wheeling.

The chopper-type power supply circuit in FIG. 1(c) uses a reactor (37)as a magnetic inductive element for a voltage-converting section (30),the stabilized direct voltage being outputted by a capacitor (46) fromthe output terminals (To), while the direct current flowing through thereactor (37) has its internal voltage drop controlled by turning thecurrent on and off using the switching element (43). A diode (45) isalso connected in this case to permit free wheeling.

In the above circuit systems, the chopper-type system in FIG. 1(c) hasthe simplest circuitry and is advantageous in making the one-chipswitching power supply device, but somewhat inferior in making theoutput voltage constant. The forward-type system in FIG. 1(b) is best interms of performance, but slightly disadvantageous for a one-chipconstruction as it requires the reactor (37) as a magnetic inductiveelement in addition to the transformer (31). The flyback-type system inFIG. 1(a) is excellent in terms of performance, and moreover, caneliminate the need for the reactor (37) since it utilizes the reactancepossessed by the secondary coil (35) in the transformer (31) to smooththe output voltage, thereby simplifying the voltage-converting section(30) and facilitating one-chip construction. From this reason, theflyback-type switching power supply device in FIG. 1(a) offers the mostadvantages in the present invention.

In applying the present invention to make a one-chip switching powersupply device in any one of the described circuit systems, all theactive elements including the switching element (43) and thevoltage-controlling section 47) are integrated into a semiconductor chip(10), which is surrounded by single-point chain lines in the figures forthe sake of convenience. In the figures in which the elements aredisposed on the surface of the chip, the active elements areinterconnected within a wiring layer (20) indicated by a larger framewith single-point chain lines, over which the magnetic inductiveelements in the voltage-converting section (30) are disposed.

There is no particular need to incorporate the rectifying circuit (41)and the capacitor (42) in the figures into the switching power supplydevice. Instead, a direct voltage may be supplied to the input terminals(Ti). Depending on the given circumstances, the stabilizing capacitor(46) on the output terminal (To) side may also be connected to the loadside of the power supply device. When incorporating the capacitor (42)or (46) into a power supply device, it is advantageous to build it intothe wiring layer (20) by utilizing the aluminum film or insulation filmrequired for that construction.

FIG. 2 shows the one-chip construction of the switching power supplydevice according to the present invention as applied to a flyback-typecircuit, corresponding to that shown in FIG. 1(a). As can be seen, theconstruction is such that the wiring layer (20) and thevoltage-converting section (30) are laminated sequentially over thesemiconductor chip (10) for an integrated circuit.

The semiconductor chip (10) used in the illustrated embodiment utilizesa dielectrically separated, or so called substrate-bonded wafer toprevent mutual interference when operating the active elements builtinto the chip. As is well known, this wafer is formed of a pair of upperand lower semiconductor substrates (1) and (2) bonded together tosandwich a silicon oxide film (3), wherein grooves are cut from thesurface of the semiconductor substrate (2) deeply enough to reach thesilicon oxide film (3) and split the substrate into varioussemiconductor regions. The groove faces are covered with the dielectricfilms (4) and filled with poly-crystal silicon (5), and the activeelements or groups of the active elements are built into respectivesemiconductor regions formed by dielectrically separating the substrate(2).

FIG. 2 shows the switching element (43), the rectifying diode (44), andn- and p-channel field effect transistors (47a) and (47b) in avoltage-controlling section (47) as the representatives of the largenumber of active elements built into the semiconductor chip (10). Theswitching element (43) for the main circuit is a vertical field effecttransistor, and the rectifying diode (44) also has a verticalconstruction. The surface of this chip (10) is covered with aninter-layer insulation film (11) made of phosphor silicate glass or thelike in order to cover the poly-crystal silicon gates from above, as isusually done.

The wiring layer (20) is formed of, as usual, a multi-layer wiringstructure, which is a lamination of the multi-layer wiring films (21)made of a metal, such as aluminum, that interconnects the elements 64selectively contacting the semiconductor layers of active elements inwindows opened in the inter-layer insulation film (11), and theinsulation film (22) made of silicon oxide film disposed between thelayers. The switching power supply device according to this embodimentis formed to slightly expand upwardly from a part of the wiring layer(20), as shown in Fig. 2, in which the capacitor (46) is built in tostabilize the output voltage. The capacitor (46) is formed of multiplelayers of electrode films (23) utilizing the same aluminum films asthose used in the wiring films (21), and thin dielectric films (24) madeof silicon oxide and sandwiched between the electrode films (23), whichare connected to the rectifying diodes (44) in the semiconductor chip(10) via the wiring films (21). Further, the uppermost layer of thewiring layer (20) is covered with an insulation film (25).

In this example of the magnetic inductive elements in thevoltage-converting section (30), the flyback transformer (31) is builtabove the insulation film (25) in the wiring layer (20). Specificconstruction examples will be explained later with reference to FIG. 3,while FIG. 2 shows only its outline briefly. The surfaces of the wiringlayer (20) and the voltage-converting section (30) are ultimatelycovered with a protection film (50) made of materials such as, forexample, silicon nitride, with openings (51) at adequate locationstherein while the aluminum of the wiring films (21) are exposed in theopenings (51) to serve as connecting pads for the input/output terminals(Ti) and (To), as shown in FIG. 1.

FIG. 3(a) shows a top view of an example of the transformer (31), andFIG. 3(b) shows a section of a line 3(b)-3(b) in FIG. 3(a). Thetransformer (31) illustrated in FIG. 3(b) is formed of the thin magneticfilm (32) at a lower side, the insulation film (33), the primary andsecondary coils (34) and (35) made of thin-film conductors, theinsulation film (36) and the thin magnetic films (32) at an upper side,which are sequentially laminated over the insulation film (25) in theabove-mentioned wiring layer (20) shown briefly. The transformer (31) isso-called shell-type construction, which forms a closed magnetic circuitenclosing the coils (34) and (35) from the outside using the lower andupper thin magnetic films (32).

As shown in FIG. 3(a), this embodiment has the primary coil (34) and thesecondary coil (35) formed in spiral forms, wherein terminals (34a),(34b), (35a) and (35b) on both sides are connected to the switchingelement (43) and the diode (44) via the aluminum wiring films (21), asshown in FIG. 2. In the example shown in FIG. 3, the primary coil (34)and the secondary coil (35) are wound 6 times and 2.5 times,respectively, resulting in winding ratio of 2.4, and are connected toeach other so that the coils will be wound in opposite directions.

These coils (34) and (35) are made of thin-film conductors made ofhigh-conductive metals, such as aluminum, copper and silver, and areformed to have a thickness from several to several tens micrometers byusing a sputtering process or a deposition process, to which photoetching that utilizes semiconductor manufacturing techniques is appliedto give the films to have a width from several tens to 100 micrometersin a spiral pattern, as shown in FIG. 3(a).

The thin magnetic films (32) are disposed so that they cover the spiralcoils (34) and (35) from above and below, while FIG. 3(a) shows only apart of them because of the illustration convenience. This thin magneticfilm (32) is a ferromagnetic metal with soft magnetism, such aspermalloy, made to a thin film with a thickness of ten to several tensmicrometers, preferably in an amorphous state, using the sputteringprocess. To keep the high-frequency loss as little as possible, slits(32a) are cut in a direction perpendicular to each turn in the coils(34) and (35). These slits (32a) are spaced from ten to several tensmicrometers.

Thus, in the present invention, the magnetic inductive elements has thelaminated structure made of the thin magnetic films and thin conductivefilms, so that it is possible to reduce the internal high-frequency lossand improve the frequency characteristics in high frequency regions withswitching frequency over 1 MHz to thereby provide high inductance valuesof about several micro H even at a high frequency of 10 MHz. Therefore,the present invention can raise the switching frequencies more thanconventionally adopted frequencies, and thereby reduce the magneticinductive element so that it can be mounted easily on a semiconductorchip (10) by reducing the size to several to 20 mm square. The totalthickness of the laminated structure can be reduced to below 100micrometers because of its thin-film construction.

The voltage-converting section (30) formed of the transformer (31) withthe above-mentioned thin-film construction is, of course, mounted orincorporated on the wiring layer (20) while the semiconductor chip (10)is still in a wafer state as shown in FIG. 2, and separated intoindividual chips after the wafer is covered with a protective film (50).Thus, the present invention makes it possible to manufacture a one-chipswitching power supply device entirely by utilizing semiconductorprocessing technology.

The switching power supply device according to the present invention isan extremely small one-chip device, and moreover, since thevoltage-converting section (30) has already been integrated into thedevice, it requires no connection via a printed wiring substrate as isrequired in the conventional constructions. For instance, the device canbe incorporated into an electronic device or an electronic circuit,while mounting on a chip and connecting to it via the connecting padsdescribed earlier, and can then be used as it is.

FIG. 4 shows an embodiment of the present invention, which isadvantageous for reducing the loss in the switching element (43) in theform of a circuit for a flyback-type switching power supply devicecorresponding to that shown in FIG. 1(a). In the embodiment of thepresent invention, the input side in the voltage-converting section (30)is only split into various parts to have the switching element (43) toturn on and off the input-side current flowing in each split inputsection independently. For this purpose, the voltage converting section(30) may be constructed with a single transformer equipped with variousinput coils. However, in the embodiment in FIG. 4, various transformers(31), about ten transformers for example, are disposed as the magneticinductive elements for the voltage-converting section (30) to haveswitching elements (43) specifically to turn the currents flowing in theprimary coils (34) on and off independently.

These various primary coils (34) have a direct voltage that has beenproduced from an alternating voltage received at the input terminals(Ti) by using the rectifying circuit (41) and smoothed by the capacitor(42) as in the case shown in FIG. 1(a), whereas the current flowing inthese parts is turned on and off simultaneously by giving a switchingcommand (SS) from the voltage-controlling section (47) to the variousswitching elements (43), while the secondary coils (35) in thetransformer (31) are all connected in series. This secondary alternatingvoltage is rectified by the rectifying diode (44) and stabilized by thecapacitor (46), and then drawn out from the output terminals (To) as adirect output voltage, as in the case shown in FIG. 1(a).

In the embodiment as shown in FIG. 4, since the current to be turned onand off by the switching elements (43) is reduced by a factor of ten,the loss in each switching element (43) is reduced in proportion to thiscurrent reduction, so that the size of the element (43) can be reducedin proportion to the current reduction. Hence, its operating speed canbe increased to reduce the loss associated with the on-off operation,particularly the turn-off loss that occurs nearly in proportion to thevolume in a depletion layer of the semiconductor region, to an extentgreater than a reduction proportional to the current reduction.

This loss-reducing effect is exhibited advantageously in frequencyregions in which the switching frequency of the element (43) is higherthan 1 MHz, especially in high frequency regions of 10 MHz or higherwhich represent the limit for the small transistors in the elements(43). As can be understood from these explanations, the embodiment inFIG. 4 is advantageous for making the switching frequency of 1 MHz orhigher to reduce the size, so that the switching power supply device canbe easily constructed in one chip.

Incidentally, a loss in the drive circuit relative to the switchingelement (43) of the output stage in the voltage-controlling section (47)tends to increase as the switching frequency rises, wherein the loss inthe drive circuit at 1 MHz is about 15% of the total loss in theswitching power supply device, while this ratio increases if frequencybecomes higher than 1 MHz. This is because, while a drive circuitusually uses a CMOS invertor circuit to turn a pair of transistors onand off alternately, there is a time in which both transistors are inon-state to flow a short-circuit current, and the time period of theshort-circuit current increases because in high frequency, thetransistors fast response performance becomes insufficient resulting inan increased short-circuit loss. Therefore, as a variation of theembodiment in FIG. 4, if frequency is higher than several MHz, it isadvantageous that a drive circuit is subordinated to each switchingelement (43) or to a group of two or three switching elements to reducethe size of the transistors in the invertor and to increase theiroperation speed to thereby reduce the short circuit loss in the drivecircuit.

FIG. 5 shows an example of the arrangement of the voltage-convertingsection (30) on the chip (10) corresponding to the circuit in FIG. 4. Inthe embodiment, the voltage-converting section (30) has ninetransformers (31), each having 2 mm to 4 mm square and being arranged ina square form, wherein the input-side capacitor (42) and the output-sidecapacitor (46) are mounted on its side, and the terminal region (60) forthe input terminal (Ti) and the output terminal (To) are disposed on theright-side periphery of the chip (10). As can be understood from thisdescription, it is necessary to considerably reduce the size of eachpart if the voltage-converting section (30) is to be constructed withvarious transformers (31). A pattern advantageous for this purpose isshown in FIGS. 6(a) and 6(b) using an embodiment for the thin-filmconductors in coils.

In the example shown in FIGS. 6(a) and 6(b), while the primary coil (34)and the secondary coil (35) in the transformer (31) are wound spirallyin the same way as in FIG. 3, the thin-film conductor is split into twoupper and lower layers to reduce the area, these layers being superposedone over the other and interconnected. FIG. 6(a) shows the pattern forthe thin-film conductor on the lower layer, while FIG. 6(b) shows theupper layer, wherein the parts common to those in FIGS. 3(a) and 3(b)are given the same numerals.

As can be seen from FIG. 3, since it is necessary to considerably varythe number of windings in the primary coils (34) and the secondary coils(35) in each transformer (31), the thin-film conductors for thesecondary coils (35) are disposed between the turns in the innercircumference and the outer circumference of the thin film conductorsfor the primary coils (34) to strengthen the magnetic coupling betweenthe coils.

As shown in the drawings, the primary coil (34) is formed so that thethin-film conductor on the upper layer in FIG. 6(b) is laminated overthe thin film conductors on the lower layer in FIG. 6(a), while theinsulation film is disposed between these upper and lower layers. Theprimary coil (34) begins from the terminal (34a) at one end on the lowerside in FIG. 6(a), moves over to the upper layer in FIG. 6(b) via thelinking terminal (34c), and ends at the terminal (34b) on the other end,wherein the number of windings shown in the example is 9.5. Moreover,the secondary coil (35) also has a thin-film conductor on the upperlayer laminated over the thin-film conductor on the lower layer. Thesecondary coil (35) begins from the terminal (35a) at one end on theupper side, moves over to the lower layer via the linking terminal(35c), and ends at the terminal (35b) on the other end, wherein thenumber of windings in the example shown is 1.5. Therefore, the ratio ofthe number of windings in the primary coil (34) to that in the secondarycoil (35) is 6.3. However, since the transformer (31) in FIG. 3 is of aflyback type, the secondary coil (35) is connected so that its windingdirection is opposite to that of the primary coil (34).

The coils (34) and (35) thus formed are sandwiched by the thin magneticfilm (32), a part of which is briefly indicated in FIG. 6(a) by finelines, in a manner similar to that shown in FIG. 3. To reduce the highfrequency loss in this magnetic circuit, fine slits (32a) may be cut inthe thin magnetic films (32) in a direction perpendicular to thethin-film conductors of both coils (34) and (35). By disposing thethin-film conductors in the coils (34) and (35) in two layers as shownin FIG. 6, the transformer (31) can be reduced, and by laminating thethin-film conductors of the lower and upper layers, the intersectionsbetween the thin-film conductors can be eliminated.

In addition, by providing the thin-film conductor for the secondary coil(35) having less winding than that of the coil (34) between the innercircumference and the outer circumference of the thin-film conductor forthe primary coil (34), the magnetic bond between the coils (34) and (35)can be strengthened to thereby raise the output from the transformer(31) as described earlier.

FIG. 7 is a cross section showing a critical part of a thin-filmtransformer or thin-film magnetic element prepared in accordance withthe present invention.

In FIG. 7, a thin-film transformer (10') is in the form of asemiconductor integrated device together with other transistor elementsand thin-film capacitors, wherein a silicon substrate (106) is formed onits surface with a silicon oxide film (105) having a thickness of 1-2micrometers, on an outer surface of which a magnetic film or core (104)having a thickness of 3-5 micrometers and a silicon oxide film (107a)having a thickness of 1-2 micrometers are formed. Furthermore, on thesurface of the silicon oxide film (107a), a metallic film with highelectric conductivity made of copper or aluminum is formed by asputtering process or vacuum deposition process, and then the metallicfilm is patterned in a spiral form to form a secondary coil or a firstthin-film coil (102) with a constant line width of W and a constantinter-wiring space of S.

Therefore, in the cross section, the secondary coil (102) appears toexist intermittently from its inner circumference toward the outercircumference, as shown in FIG. 7. Further, on a surface thereof, whilea silicon oxide film (107b) is deposited on it, a primary coil or asecond thin film coil (101) is formed in a spiral form with a constantline width of W, and a constant inter-wiring space of S. The primarycoil (101) occupies the same region as the secondary coil (102) relativeto the silicon substrate (106).

In this respect, the primary coil (101) is formed such that after ametallic film with high electric conductivity made of copper or aluminumis formed on the surface of the silicon oxide film (107b) by asputtering process or a vacuum deposition process, it is patterned in aspiral form. However, the primary coil (101) is different from thespiral form of the secondary coil (102), that is, the phase of theforming cycle of the spiral form is shifted from that of the secondarycoil (102), and all the wiring sections (101a) in the primary coil (101)are positioned between the wiring sections (102a) of the secondary coil(102). As a result, the wiring sections (101a) in the primary coil (101)are wound while being shifted from all the wiring sections (102a) in thesecondary coil (102) in a direction toward the silicon substrate (106).

In addition, a silicon oxide film (107c) is formed on the surface sideof the primary coil (101), and a magnetic film or a magnetic core (103)is formed on the surface of the silicon oxide film (107c). The siliconoxide films (107a), (107b) and (107c) have openings (not shown), whichare utilized to form connecting electrodes (not shown) for connectingthe primary coils (101) and the secondary coils (102) to therebyconstitute the thin-film transformer (10'). For the magnetic films (103)and (104), cobalt-based or iron-based soft magnetic materials havinghigh magnetic permeability are generally used.

In the thin-film transformer (10') with this construction, the primarycoils (101) and the secondary coils (102) are formed in spiral forms, inwhich the phase of the forming cycle for the wiring section (101a) inthe radial direction is different from the phase of forming cycle forthe wiring section (102a) in the secondary coils (102) in the radialdirection. Thus, all the wiring sections (101a) are completely shiftedfrom the wiring section (102a), without expanding the area occupied bythe coils on the thin-film transformer (10), and one wiring section(101a) does not face the other wiring section (102a). Therefore, thecapacity of the parasitic capacitors existing between the wiring section(101a) (the primary coil (101)) and the wiring section (102a) (thesecondary coil (102)) is very small. For this reason, even if thin-filmtransformers (10') are used in a high frequency circuit, the ratio ofelectric power passing through the parasitic capacitors is small, whichreduces the loss.

The shift width "d" between one wiring section (101a) and the otherwiring section (102a) may be set within a range of up to 0 to W (linewidth)+S (space between wiring sections) as in a variation of thisexample which will be described later.

FIG. 8(a) is a cross section view showing a critical part of thethin-film transformer or a thin-film magnetic element according to avariation of the present invention. The thin-film transformer of thisembodiment is formed with the shift width "d" of W/2, while otherstructures are identical to those in the thin-film transformer shown inFIG. 7. Hence the corresponding parts are given the same numerals, andtheir explanations are omitted.

Also in FIG. 8(a), the thin-film transformer (10a') has a magnetic filmor a magnetic core (104) formed on a surface side of a silicon substrate(106) via a silicon oxide film (105), a spiral secondary coil or a firstthin-film coil (102) formed on the magnetic film via a silicon oxidefilm (107a), a primary coil or a second thin-film coil (101) formed onthe coil surface via a silicon oxide film (107b), and a magnetic film ora magnetic core (103) formed on the coil surface via a silicon oxidefilm (107c).

In this thin-film transformer (10a'), the primary coil (101) and thesecondary coil (102) are formed in the spiral forms, in which the phaseof the forming cycle for the wiring section (101a) in the radialdirection is different from the phase of the forming cycle for the otherwiring section (102a) in the secondary coil (102) in the radialdirection. Thus, the entire wiring section (101a) is shifted from otherwiring section (102a) with a distance of W/2, and these wiring sectionsdo not completely face with each other.

Therefore, the capacity of the parasitic capacitors connected to onewiring section (101a) or the primary coil (101) and the other wiringsection (102a) or the secondary coil (102) is small, which serves toreduce power losses as well as other losses. Moreover, since one wiringsection (101a) or the primary coil (101) and the other wiring section(102a) or the secondary coil (102) partially face with each other,coefficient of the coupling between the primary coil (101) and thesecondary coil (102) is at a relatively high level.

Therefore, it is possible to selectively form the thin-film transformer(10') according to the first embodiment or the thin-film transformer(10a') of this embodiment, or the thin-film transformer (10b') and thelike, which has a shift width "d" of 3W/4 between the wiring section(101a) and the wiring section (102a) as shown in FIG. 8(b) as anothervariation of the first embodiment, and which is an intermediateconstruction between the thin-film transformer (10') and the thin-filmtransformer (10a'). The transformer can be made according to thefrequency levels in the circuit in which the thin-film transformer isused. Therefore, it is possible to set the capacities of the parasiticcapacitors and coupling coefficient to match the circuits. As a result,it becomes possible to design the circuit in a wide variety of ways.

FIG. 9 is a cross section view showing a critical part of a thin-filmtransformer or thin-film magnetic element according to a secondembodiment of the present invention.

In FIG. 9, also, a thin-film transformer (11') has a magnetic film or amagnetic core (114) having a thickness of 3-5 micrometers and formed ona surface side of the silicon substrate (116) via a silicon oxide film(115) having a thickness of 1-2 micrometers, a secondary coil (112)formed on the magnetic film surface via a silicon oxide film (117a)having a thickness of 1-2 micrometers, a primary coil (111) formed onthe secondary coil surface via a silicon oxide film (117b), and amagnetic film (113) formed on the primary coil surface side via asilicon oxide film (117c). Also, in this thin-film transformer (11'),after both the primary coil (111) and the secondary coil (112) areformed of a film made of metallic material with high electricconductivity, such as copper or aluminum, by using a sputtering processor a vacuum deposition process, they are patterned in spiral forms.

When patterning the metallic film made of copper or aluminum to form theprimary coil (111) or the secondary coil (112) in this embodiment, boththe primary coil (111) and the secondary coil (112) are formed in spiralforms, and the line width in each coil varies from the innercircumference to the outer circumference. Each coil is wound twentytimes, and has an innermost circumference radius of about 500micrometers, an outermost circumference radius of about 5000micrometers, a space between the wiring of about 5 micrometer, and athickness of about 5 micrometers.

In addition, the line width of the wiring section (111a) in the primarycoil (111) becomes wider from the inner circumference to the outercircumference as W₁₁, W₁₂ . . . W₁₄, W₁₅, and the line width of thewiring section (112a) in the secondary coil (112) also becomes widerfrom the inner circumference to the outer circumference as W₂₁, W₂₂ . .. W₂₇, W₂₈. Because the primary coil (111) and the secondary coil (112)are constructed so that their line width changing rates from the innercircumference to the outer circumference are different from each other,and therefore, the wiring section (111a) and the wiring section (112a)are staggered, and these sections do not face each other exactly. Thus,the capacity of the parasitic capacitors existing between one wiringsection (111a) or the primary coil (111) and the other wiring section(112a) or the secondary coil (112) is very small, which serves to reducethe power loss.

Moreover, since one wiring section (111a) or the primary coil (111) andthe other wiring section (112a) or the secondary coil (112) partiallyface to each other, the coefficient of the coupling between the primarycoil (111) and the secondary coil (112) is relatively high. Therefore,by optionally setting the line width changing rates from the innercircumference to the outer circumference in the primary coil (111) andthe secondary coil (112) according to the frequency levels at which thethin-film transformer is used in the circuit, the relation between thecoupling coefficient and the parasitic capacitance can be set to a levelcorresponding to the circuits, which allows the circuit to be designedin a wide variety of ways.

Furthermore, in the thin-film transformer (11') shown in this example,the primary coil (111) and the secondary coil (112) take spiral formsand the line width changing rates from the inner circumference to theouter circumference differ from each other. Therefore, if the coil drawnfrom the inner circumference is assumed to be wound "n" times (provided"n" is an integer larger than 2), the line widths W_(m),n in both coilsare expressed in W_(m),n =W (n) as a function of "n", and if thecircumferential lengths are assumed to be C_(m),n the circumferentiallengths C_(m),n are expressed by C_(m),n =C (n) as a function of "n".The suffix "m" indicates the side of the coil. Therefore, when thespiral form of each coil is shown by the relationship of thecircumferential lengths C_(m),n to the line widths W_(m),n at the "n"thround of the coil from the inner circumference and the relationship ofthe circumferential lengths C_(m),n -1 to the line widths W_(m),n -1 atthe "n-1th" round, the following expression can be used.

    (C.sub.m, n /W.sub.m, n)=k·(C.sub.m, n-1 /W.sub.m, n-1)

Accordingly, by varying "k" as a parameter to define the spiral shape inthe above general expression from 0.75 to 1.25, the thin-film coils ofdifferent spiral shapes were formed to determine the relationshipbetween the parameter "k" and the resistance (R) in each thin-film coil,and the relationship of the parameter "k" to the self-inductance L and Qvalues (omega L/R). The relationship between the parameter "k" and thespiral shapes may be described as follows. If "k" is large, extent ofexpansion of the line width W_(m), n is also large as the spiral movesfrom the inner circumference to the outer circumference when comparingexpansion of the circumferential length C_(m),n. Conversely, if "k" issmall, extent of expansion of the line width W_(m), n is also small asthe spiral moves from the inner circumference to the outer circumferencewhen comparing expansion of the circumferential length C_(m), n.Therefore, if k=1, extension in the circumferential length C_(m), ncauses the line width W_(m), n to be expanded at the same ratio. If "k"is larger than one, the line width W_(m), n on the outer circumferencenecessarily takes an expanded spiral shape.

Among the results of the discussions on each thin film coil with aspiral shape as defined by the "k", FIG. 10 shows the relationshipbetween the "k" and the self-inductance (L), while FIG. 11 shows therelationship between the "k" and the resistance (R) in the thin-filmcoil, and FIG. 12 shows the relationship between the "k" and the Q value(omega L/R) in the thin-film coil.

As a result, as shown by the solid line (21) in FIG. 10, in therelationship between "k" and the self-inductance in the thin-film coil,if "k" takes a small value, the coils are arranged more closely to eachother because the line width W is reduced at the outer circumferencehaving a greater circumferential length to contribute largely to theself-inductance. Hence, the self-inductance is increased. On the otherhand, if the "k" takes a large value, the self-inductance decreases.

Meanwhile, as shown by the solid line 22 in FIG. 11, in the relationshipbetween "k" and the parasitic resistance R in the thin-film coil, if "k"takes a value of I and the spiral shape is assumed to be a concentricshape while all the circumferences are assumed to be connectedelectrically in series, then the change rate of the ratio of thecircumferential length C_(m), n to the line width W_(m), n is in a stateclose to a value of 1 on any circumference, that is, a state in whichthe resistance values are equivalent. Therefore, the resistance R can beminimized when the value "k" is approximately one, and near the vicinitythereof, the resistance can be reduced to about 80% of what it is in theconventional thin-film coils to thereby reduce the losses attributableto the resistance R parasitic to the thin-film coils.

As a result, and as shown by the solid line 23 in FIG. 12, in therelationship between "k" and the value Q (omega L/R), when "k" takes avalue of about 0.92, the value Q is maximized, and is optimised as thethin-film coil. Moreover, by setting the value "k" in a range from about0.8 to about 1.2, that is, a range in which the ratio of thecircumferential length to the line width at "n"th round from the innercircumference in a radial direction of the thin-film coil is about 0.8times to about 1.2 times of the ratio of the circumferential length tothe line width of the "n-1"th round, the value Q in the magnetic coil isoptimised.

Therefore, according to this structure, by varying the value "k" in theprimary coil (111) and the secondary coil (112) as in the thin-filmtransformer (11'), the capacity of the parasitic capacitors across thewiring section (111a) or the primary coil (111) and the wiring section(112a) or the secondary coil (112) can be reduced. In addition, bysetting the value "k" to a range between 0.8 and 1.2, it becomespossible to ensure a high Q value for the primary coil (111) and thesecondary coil (112).

While this example has been explained where a thin-film coil having theabove-mentioned spiral shape is used for a thin-film transformer (11'),the structure should not be limited to this embodiment, and thethin-film coil may be applied to a thin-film inductor to produce athin-film inductor with a large Q value.

FIG. 13 is a cross section view showing a critical part of a thin-filminductor or a thin-film magnetic element according to the thirdembodiment of the present invention.

In FIG. 13, a thin-film inductor (12) has a thin-film coil (122) made ofelectrically conductive materials in a spiral shape formed on thesurface of the inductor via an insulation film, and a magnetic film(121) or a magnetic core formed on the surface of the thin-film coil(122), wherein this magnetic film (121) is divided equally by magneticfilm non-forming regions (123) disposed radially from a positioncorresponding to the inner circumference of the thin-film coil (122) tothe outer circumference.

In the thin-film inductor (12) with this structure, since the magneticfilm (121) is divided equally in the circumferential direction such thata position corresponding to the inner circumference of the thin-filmcoil (122) is centered, even if an eddy current is generated as a resultof the magnetic induction of the magnetic film (121), the path for theeddy current is separated. As a result, the eddy current is reduced,resulting in a reduced loss or eddy current loss in the thin-filminductor (12).

The first embodiment through the third embodiment for the typicalthin-film magnetic elements have been explained, whereas thesetechniques may be applied also to a magnetic head in addition to thethin-film transformer or the thin-film inductor. Furthermore, inconstructing these thin-film magnetic elements, the structures shown inthe first embodiment through the third embodiment may be combined.

On the other hand, the switching power supply device as described beforeis particularly suitable for mass production of stabilized power supplydevices, which have relatively small capacities from 1 W to about 10 W.As a result, in the present invention, it is possible to provide atreduced cost a one-chip switching power supply device extremely small insize, which is easy to incorporate into various kinds of electroniccircuits by using a switching frequency from 1 MHz to 10 MHz with a chipsize from several to 20 mm square, a thickness of 1 mm or less and aconversion efficiency of between 70% and 80%. Further, the sizereduction may be expected as a result of further improvement in thefuture as the switching frequency is raised.

In the present invention as described above, the one-chip switchingpower supply device is constructed in such a manner that the magneticinductive elements in the voltage-converting section are of thin-filmstructures, all the active elements including the switching elements toturn the input-side current in the magnetic inductive elements on andoff and the voltage-controlling section to intermittently control theswitching elements so that the output-side current is kept constant areincorporated into a single semiconductor chip, and the wiring layersthat interconnect the active elements and the voltage-converting sectionare laminated sequentially on the chip. As a result, the followingeffects can be obtained.

(a) To reduce the high-frequency loss, the magnetic inductive elementsis made to have the thin-film structure in the voltage-convertingsection, which is indispensable in a switching power supply device, sothat frequency characteristics of the inductance values can be improved,and the size of the elements can be reduced to be small enough to bemounted on a semiconductor chip. Hence, the switching power supplydevice can be remarkably reduced in size by adopting such a one-chipstructure.

(b) Since the voltage-converting section is mounted on a semiconductorchip integrating the active elements via the wiring layers and isconnected to the chip, problems, such as performance variance whichusually occurs in conventional printed wiring substrates, andmal-operations which are caused by incoming noise, are all eliminated,and the switching power supply device with highly uniform performance ofthe elements and high reliability can be provided.

(c) Since the switching power supply device can be manufactured entirelyby utilizing the semiconductor processing technologies without the needto assemble the device or mount the parts, mass production isfacilitated, and manufacturing costs are greatly reduced as a result ofthe rationalized manufacturing processes.

(d) Since the switching frequencies can be raised beyond theconventional limits by forming the magnetic inductive elements with thethin films, the electrostatic capacity of a capacitor can be reducedeven when it is incorporated into the switching power supply device. Asa result, the device is very small.

(e) In the embodiment wherein the input-side current is independentlyturned on and off by the switching element, by dividing the input sideof a voltage-converting section or by providing a plurality of magneticinductive elements, it is possible to raise the operation speed byreducing the current flowing in each switching element, to improve theconversion efficiency by reducing losses associated with the on-offoperations, and to further reduce the size of the switching power supplydevice by raising the switching frequencies.

In addition, in the thin film magnetic elements according to the presentinvention, it is important that the first thin-film coil is shifted fromthe second thin-film coil, for example, the first thin-film coil isspiral-shaped with the line width changing rate to be different fromthat for the second thin-film coil. Therefore, according to the presentinvention, the first thin-film coil and the second thin film coil do notexactly face to each other, so that the capacity of the parasiticcapacitors existing between these coils is small. Hence, the ratio ofelectric power passing through the parasitic capacitors is low, evenwhen the thin-film magnetic elements are used in high-frequencycircuits, and as a result, losses can be reduced without expanding theareas to be occupied by the thin-film magnetic elements.

Furthermore, in the case where the spirally shaped thin-film coil isarranged so that the ratio of the circumferential length to a line widthin the "n"th round from the inner circumference to the radial directionis within a range of about 0.8 to 1.2 times of the ratio of thecircumferential length to a line width in the "n-1"th round, theresistance values are the same on any point on the coil. Therefore, theentire resistance value in a thin-film coil corresponding to a state inwhich each resistor is connected in series comes close to a minimumvalue, losses attributable to the resistance in the thin-film coil canbe reduced without expanding the areas occupied by the thin filmmagnetic elements.

Furthermore, in case where the magnetic film as a magnetic core is splitinto various regions, an eddy current, even if generated by magneticinduction, can be reduced because a path for the eddy current flowingthrough the magnetic film is divided. Thus, the eddy current loss can bereduced.

What is claimed is:
 1. A thin-film magnetic element comprising:asubstrate with a surface, a first thin film coil made of a conductivematerial and formed in a spiral shape on the surface of the substrateparallel thereto, and a second thin-film coil made of a conductivematerial and formed in a spiral shape on the first thin-film coilparallel to the substrate, said first thin-film coil and said secondthin-film coil occupying nearly a same position relative to saidsubstrate surface, each of said first and second thin film coilschanging a line width from an inner circumference to an outercircumference, a changing ratio of the line width at the first thin filmcoil being different from that at the second thin film coil, said spiralshapes of said first and second thin-film coil being shifted slightlyaway from each other in a direction parallel to the substrate surface.2. A thin-film magnetic element as claimed in claim 1, furthercomprising insulation films situated between the substrate and the firstthin film coil and between the first and second thin-film coils.
 3. Athin-film magnetic element comprising:a substrate, and a thin-film coilmade of a conductive material and formed on the substrate to be parallelthereto, said thin-film coil being formed in a spiral shape so that aline width changes from an inner circumference to an outercircumference, and a ratio of a circumferential length to the line widthin a radial direction at "n"th round from the inner circumference iswithin a range of about 0.8 to 1.2 times of a ratio of thecircumferential length to the line width in a "n-1"th round, wherein "n"is an integer larger than two.
 4. A thin-film magnetic elementcomprising:a substrate, a magnetic core made of a magnetic film anddisposed on the substrate, said magnetic core being divided into aplurality of regions, and a thin-film coil made of a conductive materialand formed in a spiral form on the magnetic core parallel to thesubstrate, said magnetic core being radially divided so that an innerend of the thin-film coil is a center of the regions.
 5. A thin-filmmagnetic element as claimed in claim 4, further comprising insulationfilms, said insulating films being disposed between the substrate andthe magnetic core and between the magnetic core and the thin-film coil.